1. Field of the Invention
The present invention relates generally to the field of semiconductor devices housed in lead frame packages designed to be coupled to external circuitry. More particularly, the invention relates to a lead frame device in which leads are shielded from one another to reduce inductive coupling between the leads during operation of the circuitry housed within the lead frame package.
2. Description of the Related Art
A variety of applications exist for preconfigured electronic circuitry which can be integrated into larger electronic systems in a straightforward and rapid manner. Such preconfigured circuitry is commonly formed in multi-layer semiconductor devices. The devices may include memory circuits, signal processing circuits, analog-to-digital conversion circuits, and so forth. Power electronic circuitry may be manufactured in a similar manner, including such devices as power MOSFETs, insulated-gate, bi-polar transistors (IGBTs), and so forth. To facilitate handling and installation, the electronic circuitry is conveniently supported in an enclosure, often referred to as a "lead frame package." Conductive leads are electrically coupled to the circuitry within the package, and extend from the package for interfacing the circuitry with external components during installation.
Current lead frame-packaged devices often include from 3 to 50 or more leads extending from the circuit enclosure. Depending upon the circuit design, various signals are transmitted via the leads between the lead frame circuit and external circuitry with which the lead frame is interfaced. In an increasing number of applications, miniaturization of the electronic circuitry and the lead frame package has permitted a significant reduction in the size of the leads extending from the packages, and of the spacing between the leads. For example, lead spacings of less than one millimeter, and sometimes less than one half of one millimeter are not uncommon.
In addition to an increase in the number of leads utilized in lead frame packages, and the reduction in the lead size and spacing, switching rates for the circuitry housed within lead frame packages has increased substantially over recent years. For example, it is not uncommon to find switching frequencies of several hundred megahertz in currently available devices. At such high switching rates, signals transmitted through adjacent conductors extending from the lead frame device may cause interference with one another. In particular, because inductive coupling or crosstalk between the leads is typically a function of the rate of change of currents through the leads, such high switching rates may result in sufficient signal interference to cause bit errors in logic signals, or to otherwise degrade performance of the circuitry.
There is a need, therefore, for improved lead frame devices which reduce the risk of inductive interference between the leads extending from the devices. In particular, there is a need for a technique for limiting crosstalk between leads in a lead frame package, which permits spacing between the leads to be reduced, while at the same time allowing very high switching or cycle rates for signals transmitted via the leads.